The present invention generally pertains to a fifth wheel lube plate.
A common hitch for hauling large trailers is the well-known fifth wheel hitch, which has a large bifurcated bearing plate that receives a kingpin and locks it in place with one or more jaws. The kingpin is mounted on a trailer, which also has a bearing plate that rests upon and pivots on the upper surface of the hitch bearing plate to enable articulation between the trailer and its towing tractor. This pivotal action is typically aided by a layer or film of grease on the hitch surface. Because this grease is not only messy but also tends to retain dirt and dust, which cause wear, it is undesirable.
Various attempts have been made in the past to provide a lubricious surface layer for the hitch without the extensive amount of grease normally required. These efforts are believed to be largely set forth or represented by U.S. Pat. No. 5,263,856 to Huehn et al.; U.S. Pat. No. 3,174,812 to Widmer; U.S. Pat. No. 3,704,924 to Lowry; U.S. Pat. No. 3,275,390 to Franks; U.S. Pat. No. 5,066,035 to Athans et al.; U.S. Pat. No. 3,924,909 to Kent et al.; U.S. Pat. No. 4,121,853 to McKay; U.S. Pat. No. 4,169,635 to Szalay et al.; U.S. Pat. No. 4,457,531 to Hunger; U.S. Pat. No. 4,542,912 to St. Louis; U.S. Pat. No. 4,752,081 to Reeners et al.; U.S. Pat. No. 4,805,926 to Mamery; U.S. Pat. No. 6,010,141 to Huntimer et al.; U.S. Pat. No. 6,045,148 to Baumeister et al.; and U.S. Pat. Nos. 5,620,770 and 5,622,767 to Cork. Many of these designs would require total redesign of the hitch plate. Others involve fastening devices undesirably exposed on the top of the lubricious material. Some have the lubricious layer rather permanently mounted to the hitch so that replacement of a worn product is extremely difficult and costly. Structures such as that disclosed in U.S. Pat. No. 3,174,812 require special cavities in the fifth wheel and only provide a small bearing surface area considered inadequate. As a consequence of these and related shortcomings, most fifth wheel hitches in use still comprise the well-known grease-coated metal plate.
To overcome many of these problems, U.S. Pat. No. 5,522,613 issued to Heeb and commonly assigned with this application discloses a fifth wheel hitch having specially configured, interfitting lube plates mounted onto the hitch plate so as to substantially cover a maximum area of the bearing surface yet arranged to enable each lube plate to perform independently to a degree allowing localized “stick-slip” motion between the lubricious pad and the overlying trailer bearing plate. Lubricious polymer layer segments are disclosed that form replaceable segmented plates that are bonded to like configured, segmented steel backing plates. Threaded studs are stud-welded to the metal backing plates, projecting only from the bottom surface thereof with the studs extending down through orifices in the hitch plate for securing to the hitch plate by nuts. The lubricious material disclosed in U.S. Pat. No. 5,522,613 is a nylon material reinforced with embedded glass fibers or polytetrafluoroethylene embodied in a sintered matrix. The lubricious material is disclosed as being either molded onto the metal support plate and bonded in situ, or applied as a prefabricated layer and bonded to the metal support plate by an adhesive.
While nylon is a satisfactory material, it is very difficult to attach to a metal plate. Thus, structures similar to that disclosed in U.S. Pat. No. 5,522,613 have been constructed utilizing urethane, which bonds better to the metal backing plate. While such a construction works satisfactorily, it has been discovered some lubricious materials behave differently in different climates. It is desirable to utilize a material that is lubricious, economical and behaves satisfactorily in most climates.
One commercially available lube plate utilizes a relatively thick layer of fiber reinforced composite plastic. Because the lube plate utilizes only a few fasteners to hold it to the hitch plate, it has a tendency to sled around, thereby requiring a substantial pocket in the top surface of the hitch plate. This lube plate is also subject to peeling or buckling when a driver backs his tractor into the trailer and the leading edge of the trailer hits the lube plate, because the lube plate material is not very rigid and has few fasteners.
Accordingly, there is a need for a suitable lube plate construction that overcomes the problems noted above with respect to the prior art. Specifically, there is a need for a low cost lubricious sliding surface on which the trailer bolster plate articulates, that minimizes the possibility that the plastic insert may “peel” away from the top of the fifth wheel plate.